In recent years, with the advance of various portable appliances, great importance has been being placed to the development of batteries as one of the important key devices thereof. In particular, rechargeable secondary batteries, which are used in a variety of appliances including portable telephones, notebook-sized personal computers and further, in recent years, hybrid electric automobiles have been increasingly requested on the market.
The shape of batteries generally used at present is a cylindrical pillar or a square pillar.
Cylindrical pillar batteries, when used to construct a battery pack housing several batteries, give a poor space efficiency. On the other hand, square pillar batteries have a difficulty in the production step thereof though they give a high space efficiency in the pack. That is, the met hod used in laser-welding processing for sealing requires a controlling means for stabilizing the laser, additionally causing increase in production cost.
In a square pillar battery disclosed in JP-A-63-221551 or a hexagonal pillar battery disclosed in JP-A-9-266012, the battery is sealed by caulking the sealing plate with the case. In this method, however, strain develops at the corner part and hence the tightness of sealing is poorer than when a cylindrical pillar battery is sealed by caulking.